DH is a truck driver, and you will be amazed at all the little signal etc they can give eachother, they have their own whole language!!

So I do 'comunicate' with trucks, flash warnings if there is something they should know about up ahead (eg, roos or livestock on the road etc) and do the thankyou when i over take them etc..

DH gets cranky when I dont do it!! he thinks its rude not too!
My hubby is too! We have the two-way in the car and listening to all the terms used for coppers and cameras is quite amusing. I've heard them be called 'candy cars' 'plain wrappers' funny as.

As for the original question, no I don't flash my lights. I will use the two-way to warn the truckies of animals on the road or an accident, but that's it.